An introduction to ONIX metadata
https://storyfit.com/blog/onix-metadata-how-to
Another introduction to ONIX metadata
https://bookmachine.org/2015/01/22/non-technical-beginners-guide-onix-books/
And another introduction to ONIX
https://www.consonance.app/blog/a-non-technical-beginners-guide-to-onix-for-books/
Some information about what the Publishing status code number means
https://onix-codelists.io/codelist/64
ONIX information from the standards maintainer
https://www.editeur.org/83/Overview/
ONIX file naming
https://www.editeur.org/202/FTP-Filenaming/
More ONIX file naming (pdf)
https://www.editeur.org/files/FTP%20filenaming/080519-ftp-filenaming-issue-4a.pdf
Even more ONIX file naming (pdf)
https://www.editeur.org/files/FTP%20filenaming/file_naming_convention_v03.pdf
Centraal Boekhuis ONIX API information (Dutch only). New link, since CB is to disfunctional to even maintain their own namespace. Even een redirect from wiki.cb.nl to the new url is to difficult?
https://userguidescb.atlassian.net/wiki/spaces/BERDEFINTERN/pages
PHP code for parsing ONIX XML
https://github.com/chrisribal/onix-parser
More PHP code for parsing ONIX XML
https://github.com/ansas/php-onix
Perl code for parsing / importing ONIX XML
https://github.com/nbezzala/Onix